I. Technical Field
The present invention relates generally to wells, and more particularly to wireless communication systems in oil and gas wells.
II. Background Discussion
Oil and gas wells are ubiquitous in the petroleum industry. Conventional oil and gas wells may include various field devices coupled to the well for monitoring (sometimes call field instrument devices) and for control purposes (sometimes called field control devices). These field devices may be monitored and/or controlled by a controller, which is sometimes referred to as a remote terminal unit (RTU). For example, in the oil and gas context, field devices coupled to the well may monitor the liquid levels of tanks containing oil or contaminated water, and in response to measurements from the field monitoring devices, the RTU may actuate certain field control devices such as valves when the measurements indicate that the tanks exceed a predetermined level. In this example, if the RTU cannot shut off the well and the tanks overflow, there could be environmental hazards. Furthermore, in the more general control context, if the RTU is unable to control the well by shutting it on or off at the right time, then production from the well may be undesirably disrupted. Thus, the ability of the RTU to communicate with the various field devices coupled to the well is important.
In some situations, such as where the RTU and the various field devices are in close physical proximity to each other (e.g., within 15-50 feet of each other) the RTU and the field devices may be directly coupled to each other via wiring. However, there are a number of reasons why such a physical connection may not be practical or economically feasible. First, in conventional systems, where greater monitoring and control capabilities are desired, the number of field devices often increases with time making physical connection between the controller and each field device difficult and/or cost prohibitive. Second, the distances between these field devices and the RTU may be too far physically to directly connect the field devices to the RTU with wiring, even if the RTU is centrally positioned between the various field devices. This problem is only exacerbated by an increasing number of field devices. Third, even if the RTU and a field device are in close physical proximity to each other, there may be reasons why they cannot be reasonably physically connected with wiring. For example, because of the potentially flammable nature of the oil or gas from the well, caution must be exercised when routing electrical wiring between the RTU and field devices, such as by adequately burying and grounding these electrical wires. However, it may be unfeasible to dig trenches for underground burial of these wires because of piping or other underground structures that would interfere with the installation. Thus, physical connectivity between the RTU and the field devices can be challenging to implement and can pose safety hazards during installation.
In lieu of physically wiring the RTU to the various field devices wireless field devices with wireless connections to the RTU may be used. However, conventional approaches for wirelessly connecting field devices to the RTU are not without their own problems. First, since the connection between the RTU and the field device is no longer physically wired, the power normally supplied by the RTU over the physical wiring now needs to be separately supplied at each of the wireless field devices. In other words, each wireless field device now needs a separate power source. Second, because of certain industry requirements, data from the wireless field devices may be required to be reported periodically, and this may create additional power requirements for the wireless field devices. For example, the American Petroleum Institute (API) 21.1 standard requires that field data be taken once-per-second to calculate gas flow rates and, as a result, the wireless radio in the wireless field device would need to be turned on once-per-second to convey this information back to the RTU. Since the wireless radio is one of the most power hungry portions of the wireless field device, and given the number of times the radio needs to be powered on to comply with the API standard, wireless versions of field devices may end up consuming a large amount of power. This increase in power consumption may result in a consequent increase in the cost and/or complexity of each of the separate power sources. Third, notwithstanding industry standards setting forth how frequently certain well measurements are to be taken, recent industry developments have noted that making well measurements more frequently than the industry standards may help to better optimize production of the well, particularly in later stages of the well's production period. Thus, the power consumption concerns associated with how frequently well data is measured using wireless field devices may be exacerbated during the later stages of the well's production period where more detailed data is taken to optimize the well. Fourth, because of the unreliability of wireless communications, the industry is generally reluctant to use wireless field devices for critical monitoring functions (such as collecting data for gas production calculations) or for critical control functions (such as activating pumps or valves to control production from the well). Accordingly, methods and apparatuses that overcome one or more of the aforementioned problems, as well as others, are desirable.